1. Technical Field
The present invention relates to a secondary battery module, and more particularly, to a cooling structure of a secondary battery module constructed by connecting a plurality of unit batteries.
2. Related Art
Generally, unlike a primary battery which is not rechargeable, a secondary battery is capable of being charged and discharged. A low-capacity secondary battery composed of a single battery cell is used as a power source for various small portable electronic devices such as cellular phones, notebook computers, and camcorders. A high-capacity secondary battery in which a plurality of battery cells are connected to each other in a pack structure is used as a power source for driving a motor of a hybrid electric vehicle (HEV).
Secondary batteries are manufactured in various shapes. Generally, secondary batteries may be classified as a cylindrical shape battery or a prismatic shape battery, depending on the external shape of the battery.
By serially connecting such secondary batteries, a high-capacity secondary battery is constructed to be used as a power source for driving a motor in equipment such as an electric vehicle, which needs high power.
In this way, one high-capacity secondary battery (hereinafter referred to as a ‘battery module’ throughout the specification) is composed of a plurality of secondary batteries (hereinafter referred to as ‘unit batteries’ throughout the specification) which are generally connected in series.
Each of the unit batteries includes an electrode assembly having a positive electrode, a negative electrode, and a separator interposed therebetween, a case having a space for accommodating the electrode assembly, a cap assembly combined with the case to seal the case, and positive and negative terminals protruding upward from the cap assembly and electrically connected to positive and negative collectors provided in the electrode assembly.
When prismatic batteries are used as the unit batteries, in order to construct a battery module, the unit batteries are generally alternately arranged, and the positive and negative terminals are serially connected such that the positive and negative terminals which protrude upward from the cap assembly alternate relative to positive and negative terminals of another unit battery adjacent thereto.
One battery module includes a plurality of unit batteries. For this reason, it is important that the heat generated in the respective unit batteries can be easily radiated. In particular, when the secondary battery is applied to an HEV, it is important to satisfy these conditions first.
Further, when the heat cannot be efficiently radiated, the heat generated in the respective unit batteries causes an increase in the temperature of the battery module, which results in malfunction of an apparatus to which the battery module is applied.
In particular, when an HEV battery module for a vehicle is used, the battery module is charged and discharged with large currents. For this reason, depending on how the battery module is being used, heat is generated by an internal reaction in the secondary batteries, which deteriorates battery performance.
Therefore, generally, when a battery module includes a plurality of secondary batteries, more particularly, when the battery module includes prismatic secondary batteries, a battery barrier rib is provided between the unit batteries so as to maintain a gap between the unit batteries. The gap is provided for a heat transfer medium to circulate between the unit batteries. Further, these unit batteries are inside a housing, whereby the heat transfer medium for controlling the temperature of the unit batteries is provided in the housing. Thus, the heat generated in the respective unit batteries is cooled by circulating the heat transfer medium through the battery barrier rib.
However, in such a conventional cooling method, the circulating quantity of the heat transfer medium does not stay constant due to the inflow structure of the heat transfer medium of the housing. This is due to a driving condition of the battery module, a flow condition of the heat transfer medium, and a climate condition generating temperature variations between the respective unit batteries. Accordingly, the heat generated in the respective unit batteries is not evenly radiated, which results in a decrease of charging and discharging efficiency.
In addition, in this conventional cooling method, since the flow quantity of the heat transfer medium which circulates through the battery barrier ribs between the respective unit batteries does not stay constant, temperature variations between the respective unit batteries are generated. Accordingly, the heat generated in the respective unit batteries is not evenly dissipated, which results in a decrease of charging and discharging efficiency.